Such laser treatment apparatuses are used for laser-surgical methods on the eye. In doing so, the treatment laser radiation is focused such that an optical breakthrough causes changes to the tissue. The treatment laser radiation acts, for example, by photo-disruption or photo-ablation. A particularly advantageous application of these effects is found in correction of visual deficiency in ophthalmology. Visual deficiencies of the eye often result from the fact that the diffractive properties of the cornea and of the lens do not cause proper focusing on the retina. In the case of near-sightedness (also referred to as myopia), the focus of the relaxed eye is located in front of the retina, whereas in the case of far-sightedness (also referred to as hyperopia) the focus is located behind the retina. A visual deficiency can also be present in the form of an astigmatism if focusing is not effected in a focal point but with linear distortion.
For correction of visual deficiencies, it is known to suitably influence the diffractive properties of the cornea by means of treatment laser beams. Such methods are described, for example, in U.S. Pat. No. 5,984,916 and U.S. Pat. No. 6,110,166. In this case, a multiplicity of optical breakthroughs are sequentially arranged such that a partial volume is isolated within the cornea of the eye. This isolated partial volume, which is thus separated from the remaining corneal tissue, is then extracted from the cornea through a laterally opening cut. The shape of the partial volume is selected such that the diffractive properties of the cornea after removal of the partial volume are modified so that the desired correction of visual deficiencies is achieved.
In order to form the cut by sequential arrangement of optical breakthroughs, it is, of course, indispensable to generate the optical breakthroughs at exactly predetermined locations. This requires exact positioning of the laser beam in the cornea of the eye. Therefore, displacement of the eye relative to the laser treatment apparatus must be avoided or compensated for as far as possible. U.S. Pat. No. 6,373,571 and WO 0/002008A1, therefore, propose contact lenses which are placed on the cornea of the eye as adapters and immobilize the eye relative to the laser treatment apparatus. The eye is usually secured to the adapter by suction using a vacuum. Such adapter, also referred to as contact glass, performs two functions: on the one hand, it deforms the eye in accordance with the adapter's predetermined surface shape. Thus, a defined surface shape is present in the beam path of the laser treatment apparatus. On the other hand, the contact glass fixes the eye and thereby prevents displacement of the eye during therapeutic intervention.
In order to hold the contact glass securely to the eye even when the patient moves, U.S. Pat. No. 5,336,215 proposes a device of the above mentioned type, wherein the lens focusing the laser radiation is seated in a frame together with a contact glass, which frame is in turn resiliently suspended. The lens and the contact glass are thus displaceable together along the optical axis of incidence of the treatment laser radiation. Any movement by the patient will thus automatically lead to a displacement of the contact glass and of the focusing optics in the beam path. Such movement of the optics has meanwhile turned out to be disadvantageous in terms of the quality with which the treatment laser beam can be focused.
As a remedy, it might be conceivable to mount the contact glass and the focusing optics permanently and irremovably to the laser treatment apparatus. However, this approach involves the risk of the eye being damaged by by bruising when the patient moves. Such movement could either be caused by a physical movement of the patient or could occur when placing the eye in contact with the contact glass.
Therefore, it is an object of the invention to improve a laser treatment apparatus of the above-mentioned type such that the safety mechanism can reliably avoid squeezing of the eye without adversely affecting the optical quality of the laser treatment apparatus.
This object is achieved in a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a contact glass which can be placed on the eye and through which a treatment laser beam is incident, with a safety mechanism being provided which holds the contact glass movable on the housing such that the contact glass retracts when a force is directed onto the contact glass in a direction opposed to the direction of incidence of the laser beam, the safety mechanism enabling such retraction only in case of a force which exceeds a limit value of force and holding the contact glass fixed at a force which is below the limit value of force.
According to the invention, the object is further achieved by a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a beam deflecting unit which variably deflects a treatment laser beam about at least one axis; focusing optics arranged following the beam-deflecting unit and focusing the laser beam along an optical axis into or onto the eye; a contact glass which is arranged following the focusing optics and can be placed on the eye, and a safety mechanism holding the contact glass movable in such a manner that it retracts when a force is directed onto the contact glass counter to the direction of incidence of the laser beam, wherein the beam-deflecting unit is arranged in the entrance pupil of the focusing optics, with respect to a deflecting element being effective for said one axis of deflection, and the safety mechanism couples the contact glass, the focusing optics and the deflecting element such that, during retraction, the deflecting element remains in the entrance pupil and the length of the light path between the deflecting element and the contact glass is constant.
According to the invention, the object is also achieved by a laser treatment apparatus for ophthalmic surgery, said apparatus comprising a contact glass which can be placed on the eye and through which a treatment laser beam is incident, and a safety mechanism holding the contact glass movable in such a manner that it retracts, when a force is directed onto the contact glass counter to the direction of incidence of the laser beam, wherein the safety mechanism comprises a detecting unit, which monitors retraction of the contact glass and which interrupts laser treatment operations of the laser treatment apparatus in case of a contact glass movement exceeding a threshold value.
Thus, the invention fundamentally deviates from the concept pursued by the prior art, which consists in compensating for any eye movements by a resilient support of the contact glass, and provides a contact glass which is rigid under certain basic conditions. In a first version of the invention, this rigidity is embodied such that the contact glass is movable only above a limit value of force. Thus, optimal optical conditions are ensured during irradiation of the eye with the treatment laser beam, and at the same time, compression of the eye is prevented, because the limit value of force causes a sort of panic release mechanism.
In another version of the invention, the rigidity of the contact glass does not relate to the eye, but to the mutual position of the contact glass, the focusing optics and the deflecting element. The coupling of the safety mechanism having this effect now allows movement of the contact glass due to eye or head movements of the patient, but now these movements have no effect on the optical properties of the focusing of the treatment laser beam.
In a third version of the invention, the rigidity of the contact glass provided for according to the concept of the invention is achieved in a functional manner. Laser treatment operation is interrupted if the contact glass is moved beyond a certain maximum amount.
Thus, the above-mentioned solutions provided by the invention realize different variants of the same inventive concept, namely to cause rigidity of the contact glass by means of a safety mechanism, said rigidity preventing unwanted defocusing or faulty positioning of the treatment laser radiation by eye movements or head movements. As mentioned above, said rigidity can be realized either structurally, with respect to the eye or the optics of the laser treatment apparatus, or functionally. These three approaches will be referred to hereinafter as the first variant (retraction of the contact glass above a limit value of force), the second variant (coupling of the contact glass, the focusing optics and the deflecting element) and the third variant (abortion of laser treatment if a movement of the contact glass exceeds a threshold value), respectively.
All three variants have in common that they prevent bruising of the eye. If there is danger of bruising, the contact glass and the patient are moved apart. This fact is referred to herein as retraction. This means, on the one hand, that the contact glass as well as possibly further parts of the laser treatment apparatus are moved away from the desired position of the patient. On the other hand, this term, of course, also covers a kinematically reversed approach, wherein the patient is moved away from the contact glass. From the patient's view, this is also a retraction of the contact glass, which justifies the generalization made herein.
Of course, the variants of the invention can also be combined with each other. This also applies to any embodiments and improvements.
In the first variant of the invention, an increase in the pressure which the patient exerts on the laser treatment apparatus, for example by his eye, only leads to a retraction of the contact glass if the limit value of force has been exceeded. Bruising of the eye is excluded if a suitable limit value of force is selected, and at the same time optimal operation is achieved under normal conditions.
In a particularly simple construction, the limit value of force is caused by an elastic force or weight force. One possibility of achieving this, is, for example, an elastic support for the patient on a bed, which support is selected such that the patient's bed retracts upon an apparent increase in the patient's weight. An increased pressure of the eye on the contact glass manifests itself in such apparent increase in the patient's weight so that the desired retraction then occurs. The laser treatment apparatus or the optical component of this apparatus can remain spatially fixed. Instead of the described possibility of mechanical compensation, a corresponding closed-loop control can also be effected, of course, e.g. in the form of electronic closed-loop control.
In a kinematically reversed construction, which is comparatively more simple in mechanical terms, it is advantageous to mount the contact glass to a holding element, which is pressed against a stop of the housing by a force defining the limit value of force. In case of a contact pressure force exceeding the limit value of force, the contact glass can then be displaced relative to the housing so that the desired safety features are achieved. Retraction is then effected by the contact glass; the bed need not be moved for this purpose.
This can also be combined by mounting a force sensor to the holding element but effecting retraction through movement of the bed.
In an advantageous further embodiment of the invention, laser treatment can be continued even if the contact glass retracts, as long as certain basic conditions are complied with. For this purpose, retraction not only of the contact glass, but also of the relevant components of the optics by which the treatment laser beam is focused into or onto the eye is convenient. Therefore, the holding element which is mounted to the contact glass may also carry focusing optics which focus the treatment laser beam into or onto the eye. When retracting, the contact glass and the focusing optics then move together.
The limit value of force is conveniently set such that bruising of the eye is definitely prevented. A suitable value for this purpose is approximately 1N.
The first variant of the invention is suitable not only to prevent damage caused by a patient's fault, but apparatus malfunction can also be checked thereby. During laser treatment, the patient is usually supported on a bed. A height adjustment unit allows adjustment of the distance between the laser treatment apparatus or the contact glass, respectively, and the patient. The safety mechanism according to the invention reliably prevents malfunction of this height adjustment mechanism resulting in bruising of the eye. If, for example, the height adjustment mechanism moves the patient too far towards the contact glass, the safety mechanism automatically causes retraction of the contact glass before there is a risk of the eye being squashed.
The second variant of the invention ensures that retraction of the contact glass has as little effect as possible on the optical quality with which the treatment laser radiation is introduced into the eye. Since in a laser treatment apparatus the laser treatment beam is guided to a great diversity of points (e.g. during the above-mentioned correction of visual deficiencies), three-dimensional shifting of the focus of the laser beam is usually required. This regularly requires deflecting elements in the form of two scanners, for example galvanometer scanners, for lateral movement of the laser focus.
In a simple construction, optical errors which occur during retraction of the contact glass can be minimized by rigidly connecting the contact glass and the focusing optics which focus the treatment laser beams into the eye such that they retract together. If a beam path section which is insensitive to changes in the length of the optical path, for example a parallel or near parallel beam path, is additionally arranged preceding the focusing optics, the optical errors occurring during retraction of the unit consisting of the focusing optics and the contact glass are automatically small.
In order to minimize errors induced by retraction of the contact glass, it is generally advantageous if the length of the light path following the deflecting element remains unchanged even during retraction. Otherwise, the distance in a projecting lens would change, which would be equal to a change in the effective focal length of the entire system. In particular, curved contact glasses, which have a concave curvature on the side facing towards the patient and which thus only add little to the internal pressure of the eye, would be difficult to use. Instead, contact glasses would have to be used, which flatten the front surface of the eye and are, therefore, disadvantageous with a view to keeping the internal pressure of the eye as constant as possible. Therefore, further minimizing is achieved if the contact glass, the focusing optics and at least one of the deflecting elements of the beam-deflecting unit are connected to form one single unit, and the safety mechanism causes longitudinal guiding of this unit.
The second variant of the invention then keeps the distance between the deflecting unit and the focus of the treatment laser radiation constant. If the axial position of the laser focus were shifted, unpredictable side effects could appear in the patient's cornea. In the worst case, a laser effect could even damage the epithelium or the endothelium.
The deflecting elements, e.g. AOD or scanners, are favourably arranged in pupil planes of the optics. In most cases, they effect beam deflection about two mutually perpendicular axes. However, other approaches, e.g. using a tumbling mirror, are also possible, if they effect 2-dimensional beam deflection. Common scanners operate by reflection at surfaces which are variable with respect to their clearance angle relative to the beam path. This has the effect that the entire beam path is folded at an angle at the scanners. In doing so, folding angles of approximately 90° are preferably realized. It is advantageous to design one of said bends such that part of the optical system is supported there rotatable about an axis. Retraction of the contact glass can then be achieved by rotating the optical system about said bend, so that the subsequent beam path is only pivoted, in principal, but otherwise does not change. If another deflection of the beam path, e.g. by 90°, is provided at this bend, retraction of the contact glass is realized as a pivoting movement about the axis of rotation located in the first bend. This enables pivoting of the subsequently arranged optics about the bend and, thus, a retraction of the contact glass without any changes appearing in the beam path.
Therefore, it is preferred that the light path of the laser beam be deflected at least once following the entrance pupil of the focusing optics and that the safety mechanism cause a joint rotary or pivoting movement of the contact glass, the focusing optics and the deflecting element during retraction. A particularly convenient construction is one in which the contact glass, the focusing optics and the deflecting element are rigidly connected to form an arm and the safety mechanism comprises a rotary support for the arm with the axis of rotation in the plane of the deflecting element. The arrangement of the axis of rotation at the deflecting element has the advantage that, during rotation or pivoting, no disadjustments are generated with respect to deflection.
However, a weight compensation may be necessary, because the rotary or pivoting movement requires the entire optical unit to be raised from the contact glass up to the pupil with the deflecting element. Therefore, it is favourable for this embodiment to provide corresponding balancing weights, reducing the force required to raise the arm and thus to retract the contact glass.
This embodiment is a variant of a generally preferable safety mechanism comprising a weight force compensation unit, in particular in the form of a counterweight or a spring element. If it is desired to combine the advantages of the first or second variants, the weight force compensation unit can conveniently set the limit value of force. In particular, it is possible for the arm to be supported by the housing of the laser treatment apparatus at the limit value of force.
Another approach involves placing the axis of rotation in the beam path at the location of the weight center of gravity, because, in doing so, a balanced structure and, consequently, a low force for the retraction of the contact glass is automatically achieved.
In the third variant of the invention, a detecting unit is provided for functional rigidity of the contact glass, which unit blocks the laser treatment operation upon a contact glass movement exceeding a threshold value. In this case, the threshold value can be selected according to different criteria. Depending on the design of the laser treatment apparatus, the threshold value can be selected in the sense of an emergency deactivation, which deactivates just before an inadmissibly great load on the eye, or may serve as a quality-ensuring feature and may consider the optical errors caused by said movement.
If the threshold value is selected such that it should prevent an inadmissibly high eye pressure, deactivation is effected before retraction of the contact glass reaches a mechanically determined end of said movement. Even after the threshold value has been exceeded, counter measures can still be initiated without the contact glass abutting at the end of its movement. For example, a height adjustment mechanism of the patient's bed can be deactivated or the patient's bed can be quickly lowered.
Thus, one of the counter measures consists in actively moving the contact glass and the eye apart. Therefore, it is preferred that the safety mechanism comprise a drive for active retraction of the contact glass and that a control unit control the drive to actively retract the contact glass in case of a force exceeding the limit value of force or a contact glass movement exceeding the threshold value, respectively.
In the case of the above-mentioned rotatable or pivotable optical arrangement of the second variant, the drive will usually initiate a pivoting or rotary movement, in particular rotating the arm mentioned above with respect to the second variant.
The detecting unit may use a light barrier located near a mechanical stop for the path of movement of the contact glass. Of course, a multi-level stepwise response detecting unit or continuous monitoring of the position of the contact glass is also possible according to the invention.
One possibility of additionally detecting that a desired maximum movement is exceeded consists in sensing at the mounting mechanism by which the eye is fixed to the contact glass. For this purpose, a vacuum is conventionally used. The detecting unit may then sense the pressure in the vacuum system and thus determine an inadmissible movement of the eye relative to the contact glass.
Due to the human physiognomy an eye movement directed towards the contact glass automatically involves a movement of the head. Therefore, it is possible to sense the force directed towards the contact glass not only at the eye, but also at the patient's body, preferably at the head. This procedure gives further protection to the eye. Therefore, it is convenient for all the above mentioned variants if a supporting unit is provided comprising a support that can be applied to the patient's body and is coupled to the safety mechanism such that a certain force on the support opposed to the direction of incidence of the laser beam also causes retraction of the contact glass. In the third variant, the detecting unit may detect pressure on the support.